In recent years, semiconductors including compound semiconductors are further expanding their application range by making use of various characteristics thereof. For example, the compound semiconductors are particularly useful as an underlying substrate for epitaxial growth for fabrication of high-speed devices, optical communication devices, and microwave devices.
When a semiconductor (including a compound semiconductor) is used as the underlying substrate for epitaxial growth, a surface of the semiconductor needs to be a mirror surface without distortion. For this reason, after so-called “preprocessing” such as cutting, lapping, or etching of a single-crystal ingot of the semiconductor, a resultant wafer is normally mirror-polished.
A known method of this mirror polishing is, for example, to polish the surface of the semiconductor wafer with a polishing agent containing colloidal silica (e.g., Patent Document 1 below) and thereafter clean the surface with pure water.
However, when devices were manufactured using a multilayer body in which an epitaxial layer was laid on the semiconductor substrate obtained as described above, there was the disadvantage that it was difficult to achieve a good yield, and therefore there were earnest desires for development of a semiconductor substrate free of the disadvantage.    Patent Document 1: Japanese Patent Application Laid-open No. 64-87147    Patent Document 2: Japanese Patent No. 3183335    Patent Document 3: U.S. Pat. No. 6,488,767    Patent Document 4: U.S. Pat. No. 6,951,695    Patent Document 5: Japanese Patent Application Laid-open No. 2006-310362    Patent Document 6: Japanese Patent No. 2599250